Leachability of metals from municipal solid waste flyash and bottom-ashes at different pH

The generation of municipal solid waste (MSW) has reached 50 million tonnes per year since 1985 due to the growing economy in Japan. Due to limited availability for land space, this huge amount of waste is reduced by incineration, with the residue of fly ash and bottom ash disposed in controlled landfills. A compacted low hydraulic conductivity of <1×10^-8 m/s and chemical compatible clay liner is in place under the polyethene liner in the landfill site. The focus of this paper is the teachability of heavy metals from MSW fly ash and bottom ash at different pH to simulate the worst situation such as acid rain. This work investigates the elements present in the MWS fly ash and bottom ash, and the leachibility of heavy metals from both fly-ash and bottom ash. XRF, XRD and ICP are used to characterize the ashes. The teachability of metal ions and anions is evaluated using repeated batch-leaching and column-leaching tests. The results are used to estimate the short- and long-term environmental impact of MSW fly ash in landfill sites and to provide information for the design of thickness and required hydraulic conductivity of landfill soil liners. The results of this study indicate that the fly ash and bottom ash consist of mostly of Si, Na, Ca, Mg, Fe, Zn, Cu, and Pb. The leaching activity to some degree depends on the pH of the leaching solution. Repeated batch leaching tests indicate that the leachabilities of MSW flyash at pHs from 3 to 6 were very similar. Heavy metals such as Pb, Zn, Cu leached at low concentrations. The MSW ashes have high buffer capacity. The pH of leachates for the washing solution of pH 3, 4, 5, and water were between 10 and 11, except for the pH of the leachate for a pH2 washing solution, which dropped from 11 for the first washing to 3.5 for the 80th washing. Column leaching tests of fly-ash and bottom-ash indicate that the concentrations of leached Pb>Zn>Cu in water leaching and effluent pH remain as high as 11. With the pH 2 leaching solution, as the buffer capacity of the ashes decreased Zn and Cu leached much more than Pb.